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Reviewer: Srajan Ebaen
Financial Interests: click here
Source: Ancient Audio Lektor Prime, Apple iMac 1TB with AIFF files up to 24/192, Pure Music 1.7, Weiss DAC2, Burson Audio HA-160D
Preamps: Esoteric C-03, ModWright DM 36.5, Bent Audio Tap X, Yamamoto AT-03-1A [on loan]
Amplifiers: Yamamoto A-09S
Speakers: ASI Tango R, Zu Essence
Cables: Complete loom of ASI Liveline, Furutech GT2 and WireWorld Starlight 5² USB A-to-mini-B cables [on loan], LaCie and Entreq Firewire 800 cables, Entreq USB cable, Black Cat Cable Veloce S/PDIF cable [on loan]
Stands: 2 x ASI HeartSong 3-tier, 2 x ASI HeartSong amp stand
Powerline conditioning: 1 x Walker Audio Velocitor S, 1 x Furutech RTP-6
Sundry accessories: Extensive use of Acoustic System Resonators, noise filters and phase inverters, Advanced Acoustics Orbis Wall & Corner units
Room size: 5m x 11.5m W x D, 2.6m ceiling with exposed wooden cross beams every 60cm, plaster over brick walls, suspended wood floor with Tatami-type throw rugs. The listening space opens into the second storey via a staircase and the kitchen/dining room are behind the main listening chair. The latter is thus positioned in the middle of this open floor plan without the usual nearby back wall.
Review Component Retail: ¥500.000 with output tubes, ¥380.000 without

Built around NOS bottles—remaining inventories of tubes no longer made which date from the middle of the last century—Shigeki Yamamoto's new A-010 stereo SET is somewhat of a statement by a Japanese tube maniac. A corporate firm like Swiss Nagra Audio for example would never commit to any tube amplifier platform which couldn't be serviced by current-production valves. The spirit at Yamamoto SoundCraft is different. Like some fancier of rare orchids who digs up specimens from a dense Micronesia jungle to enjoy their fragrance at home, Shigeki goes after exotic power triodes like the AD1, 101D, 104D and 205D. He first carefully evaluates their sonic potential, then acquires a private cache sufficient to support ownership of limited production amplifiers built around these valves. The obvious target audience are like-minded tube maniacs who value the opportunity to once again delight in the unique auromas of such forgotten tubes.
Yamamoto's active exhibit at the 2010 Akihabara Vacuum Tube Fair

To participate in this exclusive game doesn't require the deepest of purses—all of Yamamoto's creations are fairly priced and considering their hand-crafted status and quality of construction good values—but a combination of highly efficient speakers, smaller playback venues and/or civilized volumes. That's because power output of these amps tends to be less than there are fingers on one hand.

For the 3-watt A-010, Yamamoto's chosen power triode became the VT-52. It can still be found made by (or branded as) Hytron, Philco, Raytheon, Senco, TungSol and Western Electric. Amongst them circulate two different specimens with 6.3V and 7V filaments. Of interest to Yamamoto was the latter branded Western Electric. The 7V/1.18A VT-52 seems to have been a military version of the 2C45 which itself was a derivative of the classic 45. Western Electric had National Union under contract to manufacture their 2C45. The current consensus seems to be that the only equivalents for the VT52 are the 45 Special and 38142. The VT52 is thus considered a Super 45 of sorts. Shigeki specifically regards the A-010 amplifier as an evolution and step-up from his prior 45-based A-08S platform. Or as he put it, "this machine was designed to demonstrate the performance of the VT-52 to its maximum extent".

As such the designer retained the 10.000-hour C3m drivers and 80* rectifiers we already saw in his 45 amp—the same drivers also feature in my big A-09S 300B version—but he then doubled up on the 80s. With the A-010 we thus have four rectifiers on deck. These supply the pentode drivers and direct-heated power triodes so that each gets its own power supply. This division of labor minimizes the 'pulling down' action which high voltage swings with their concomitant current rises in the output tubes have on the driver tubes. It also allowed optimization of the discrete power supplies for each tube type. The C3m rectifier for example could benefit from a smaller 2uF film cap with an US-issue Ixys current regulator while the output filter choke on the VT-52 was eliminated to retain just a basic RC filter. These changes "improved the amplifier's operational speed".
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* The 80 uses a UX-4 base and is electrically equivalent to a 5Y3GT.

DC heaters with Mosfet current sources maintain good noise performance while mains power is processed by two R-core power transformers. One supplies the high-tension circuit, the other the heater supplies. It's divide and conquer again. The output transformers are cut-core high-B types with 100-micron core laminations in Teflon paper insulation. These custom-made cores are said to offer very low-loss highly linear magnetic permeability. A familiar Yamamoto solution are the epoxy-resin damped polypropylene film coupling capacitors encased in Ebony. US firm Dale once again became the favored supplier of precision resistors. Specifications are a 0.4V input sensitivity for full output with a high overall gain of 24.5dB**. Input impedance is 200Kohm, weight 16.3kg and dimensions are 400 x 314 x 211mm WxDxH. As is standard Yamamoto practice, auto bias requires no user adjustments. The in-house built precision meter—a toggle switch selects between left and right VT-52—merely confirms proper tube operating condition. The owner can easily see when the power triodes no longer bias up properly to require replacement. This should be standard on all auto-bias amps but sadly isn't.
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** A recent Swiss wine & cheese presentation by Nagra Audio, of their new 300p amplifier in a sizeable hall of Château d'Aigle with Verity Audio speakers, showed their amp's modulometer at 0.2-watt output with 2-watt peaks when playback levels of a Jacques Loussier Mozart Piano Concerto N°. 20 were just right. While Yamamoto's 3-watt rating does impose obvious restrictions in speaker choices, most consumers are sadly misinformed about their actual power requirements. Combine the A-010's circuit gain with a hi-gain source like my 5.5V-max Weiss DAC2 for example and you could do serious damage with even standard 90dB speakers and a passive preamp. Granted, loudness alone never equates with optimum drive and control. Particularly low-frequency peaks should cause clipping over most regular speakers whilst running a no-feedback SET to its power limits will seriously increase its harmonic distortion. Even so, common concerns that such amps can't play loud enough unless one had 110dB horns, tiny rooms or only played string quartet adagios are somewhat irrational.



The above photo of Mr. Yamamoto is compliments of German Yamamoto importer Jacmusic.com. Shigeki returns the trade favor by importing Jac van der Walle's excellent Emission Labs tubes to Japan. Unlike the EML solid-plate 45 and 300B-XLS which became my favorite power tubes in the A-08S and A-09S Yamamoto amps, the VT-52 of the A-010 is currently only available as new-old stock. EML does however make a modern 80 rectifier [see left] to give valve rollers something to play with.


Further signature Yamamoto flourishes for the A-010 amplifier are the Japanese Asada Cherry deck which is vacuum impregnated with resin to acquire Bakelite properties; the belly pan beneath it to hide the guts; the proprietary Teflon tube sockets, RCA sockets and speaker terminals all made in Yamamoto's machine shop—Shigeki's professional background is as precision machinist and his tube sockets appear in some of the most expensive valve amps made—; the turned Ebony footers; the back-lit power switch on deck; and the matte gold-anodized transformer cover flanked by Cherry cheeks.


Also solid Yamamoto tradition is operating the A-010 in class A single-ended without negative feedback. Push/pull and class A/B don't belong in this context. When Mr. Yamamoto embraces pentodes as he does for the German telephony Siemens drivers—these he cuts out from their stock metal canisters so attention must be paid to align his silk-screened arrow for proper pin orientation—they never show up in the output stage..

To recap, the A-010 is the latest micro-power stereo SET from one of the most popular such boutique operations in Japan. Its pièce de résistance is a little-known direct-heated power triode for which no currently manufactured tube equivalent exists. As such this amp is a bit of a Tibetan tulku.

It's a new body for an old soul not seen in this realm for quite some time.
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